Re: [libvirt] Proposal: no dnsmasq (no dhcp and no dns) and no radvd option

On 11/25/2012 08:25 AM, Gene Czarcinski wrote: disableDhcp already exists - you just don't have a <dhcp> section (and if you do have a <dhcp> section, it seems very illogical that you would want dhcp disabled). disableRA may be a valid concern, since that's on by default if there are any IPv6 addresses. However, to pull the discussion back in - I had earlier suggested *not* having an attribute called "disableXXX" because it starts to get confusing - you're saying "Yes, I don't want this feature.". It's simpler to understand "*No*, I *don't* want this feature". And I'd also suggested making it an option of the already existing <dns> element (see below). I like "<dns log='xxx'.../>" (edit: I may have changed my opinion on this - see the end of the message) Why? That would only make sense if it was a placeholder that could be modified later to do something (and even then only if it would be impossible to just start it at a later time instead). I dislike that idea - it give two ways to specify the same thing, which is bad. Experience has shown that it's better to have a single way to specify each thing; that way there is no ambiguity when doing a parse->format->parse cycle. Remember that you can easily have no dnsmasq daemon by simply specifying: <dns enable='no'> and then having no <dhcp> element anywhere. As for RA, that will require an option to turn off. We currently only start radvd if networkRadvdConfContents returns a non-NULL string, and it is *perfectly* setup to have an "enableRa='yes|no'" (with default of 'yes') on each IP address - it would simply not append the lines for an IP address to the conffile string if that IP's enableRa was no. So, if all the ipv6 addresses had enableRa='no', radvd wouldn't be run (and I'm sure you could do something similar for the ra implementation in dnsmasq). An indicator that something more than just log='yes|no' may be desired. Yes, that's definitely a no-go. I'm pretty sure nobody would stand for that. If that's how dnsmasq operates, we can't switch to using dnsmasq until that's remedied. That will be good, but since it will be something not detectable from the --help output, it will mean that use of dnsmasq for RA will need to be dependent on an "even later" version of dnsmasq. Because some people want libvirt-created networks, but want to manage the firewall rules themselves. (btw, you must be running with net.bridge.bridge-nf-call-iptables=1, otherwise communications between guests (ipv4 and ipv6) would work just fine with no extra rules) Yes, exactly. The network would have no rules of its own (or maybe a ruleset to allow only incoming, as is currently the case for a NATed network), and each guest's interface could override that with its own rules to allow incoming. More appropriate than what? Than using a <filterref> in each guest's interface? Or more appropriate than making it an option of <forward>? I think it makes sense to have this be an option of <forward>, because it is controlling exactly what traffic is allowed to be forwarded. And when you look at the existing forwarding modes: <forward mode='nat'> It doesn't make sense to have different levels of filtering for a NATed network, because the filter rules are required for NAT to work at all, and due to the way NAT works, incoming sessions are impractical anyway: none - nonsensical (if you're not going to allow any traffic in-out, then why have <forward> at all?) open - nonsensical (incoming sessions can't work without additional forwarding rules anyway) restricted - that's what it does anyway <forward mode='bridge|hostdev'> These networks have nothing managed by libvirt anyway <forward mode='none'> (i.e. "no <forward> element) By definition if you have this type of network, you don't want to allow any traffic in or out of the network (heck, we even run dnsmasq with different options so that the dns server won't forward requests for unknown hosts). <forward mode='route'> This is the *only* type of forwarding where it makes sense to offer different options for the stock filters provided by libvirt. none - the host admin will be managing filters themselves external to libvirt. open - this is what it currently does - allows incoming and outgoing sessions restricted - this would be similar to what is currently done in NAT mode (allow outgoing sessions but not incoming), but without the extra mangling rules to NAT the packets. Since the different filtering options only make sense for forward mode='route', it's sensible to put the option in the <forward> element. But that's really a separate topic that I didn't originally intend to get entwined with the dns/ra/logging things we're talking about now... As I implied above, I don't think there is any purpose to it. If you want to consolidate options, rather than grouping according to <logging> and <options>, why not put the dhcp-related options in the <dhcp> element (edit: see below - I think I've changed my mind about <dhcp>), and the dns-related options in the <dns> element as I originally proposed. I can't think of any reason why (especially considering that the <dns> element already exists as a direct sub-element of <network> that this: <network> <dns enable='no'/> or: <network> <dns log='yes'/> <!-- or perhaps use "debug|info|warn|error|none" or something --> is any worse than this: <network disableDns='yes'> or <network logDns='yes'> or this: <network> <option disableDns='yes'/> or <network> <logging dns='yes'/> or even this: <network enableDns='no'> or <network> <option enableDns='no'/> Rather, I would argue that it is *better* to put dns-related options in the already-existing <dns> element. Why create a new element that mixes the options of different functions when an element for each of those functions already exists. 1) I think dns should be disabled with "<dns enable='no'/>". The element already exists, and is the perfect place to add dns-related options (that is *why* it exists) 2) disabling IPv6 RA should be done by having <ip family='ipv6' .... enableRa='no' ...> in each ipv6 ip address element - if all ipv6 addresses have enableRa='no', then radvd (or the ra in dnsmasq) won't be run. 3) we don't need any option to disable dhcp - that's what happens if there are no <dhcp> elements. 4) I think I've changed my mind about logging options - these options would need to be set on at least a network-wide scale, but while there is a perfect existing element for that for dns, the <dhcp> and <ip> options are one-per IP address, which would lead to ambiguity and/or conflict. Beyond that, there is no existing example of setting logging level anywhere in libvirt XML - the only logging controls are done in the environment or via libvirtd.conf, and I don't know that either of those places are appropriate either. So I think we should separate that off and discuss it separately.